Off-Cut Substrates In Inverted Metamorphic Multijunction Solar Cells

Abstract

A method of forming a multijunction solar cell including an upper subcell, a middle subcell, and a lower subcell, including: providing a substrate having an off-cut of 15° from the (001) plane to the (111)A plane for the epitaxial growth of semiconductor material; forming a first solar subcell on the substrate having a first band gap; forming a second solar subcell over the first solar subcell having a second band gap smaller than the first band gap; forming a grading interlayer over the second subcell layer, the grading interlayer having a third band gap greater than the second band gap; and forming a third solar subcell over the grading interlayer having a fourth band gap smaller than the second band gap such that the third subcell is lattice mismatched with respect to the second subcell.

1 . A method of manufacturing a solar cell comprising:
 providing a first semiconductor substrate which is off-cut from the (001) crystal plane by at least 6° towards the (111)A plane;   forming a first subcell on said substrate comprising a first semiconductor material with a first band gap and a first lattice constant;   forming a second subcell comprising a second semiconductor material with a second band gap and a second lattice constant, wherein the second band gap is less than the first band gap and the second lattice constant is greater than the first lattice constant; and   forming a lattice constant transition material positioned between the first subcell and the second subcell said lattice constant transition material having a lattice constant that changes gradually from the first lattice constant to the second lattice constant.   
     
     
         2 . A method as defined in  claim 1 , wherein said transition material is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the first subcell and less than or equal to that of the second subcell, and having a band gap energy greater than that of the second subcell. 
     
     
         3 . A method as defined in  claim 1  wherein the transition material is composed of (In x Ga 1-x ) y Al 1-y As, with x and y selected such that the band gap of the interlayer remains constant at approximately 1.50 eV. 
     
     
         4 . A method as defined in  claim 1 , wherein said first subcell is composed of an GaInP, GaAs, GaInAs, GaAsSb, or GaInAsN emitter region and an GaAs, GaInAs, GaAsSb, or GaInAsN base region. 
     
     
         5 . A method as defined in  claim 1 , wherein the second subcell is composed of an InGaAs base and emitter regions. 
     
     
         6 . A method of forming a multifunction solar cell comprising an upper subcell, a middle subcell, and a lower subcell, the method comprising:
 providing a first substrate for the epitaxial growth of semiconductor material which is off-cut from the (001) plane by at least 6° towards the (111)A plane;   forming an upper first solar subcell on said off-cut substrate having a first band gap;   forming a middle second solar subcell over said first solar subcell having a second band gap smaller than said first band gap;   forming a graded interlayer over said second solar cell; and   forming a lower third solar subcell over said grading interlayer having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell.   
     
     
         7 . The method as defined in  claim 6 , wherein the graded interlayer has a third band gap greater than said second band gap. 
     
     
         8 . The method as defined in  claim 6 , wherein said graded interlayer is compositionally graded to lattice match the middle subcell on one side and the lower subcell on the other side. 
     
     
         9 . A method as defined in  claim 1 , wherein said transition material is composed of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the middle subcell and less than or equal to that of the bottom subcell, and having a band gap energy greater than that of the middle subcell. 
     
     
         10 . A method as defined in  claim 1  wherein the transition material is composed of (In x Ga 1-x ) y Al 1-y As, with x and y selected such that the band gap of the interlayer remains constant at approximately 1.50 eV. 
     
     
         11 . A method as defined in  claim 1 , wherein said first subcell is composed of an GaInP, GaAs, GaInAs, GaAsSb, or GaInAsN emitter region and an GaAs, GaInAs, GaAsSb, or GaInAsN base region. 
     
     
         12 . The method as defined in  claim 6 , wherein the first substrate is composed of GaAs. 
     
     
         13 . The method as defined in  claim 6 , wherein the off-cut angle is approximately 15°. 
     
     
         14 . A method as defined in  claim 6 , further comprising depositing a contact layer over said third solar subcell and making electrical contact therewith. 
     
     
         15 . A method as defined in  claim 14 , further comprising attaching a surrogate second substrate over said contact layer and removing said first substrate. 
     
     
         16 . A method as defined in  claim 9 , further comprising:
 patterning said contact layer into a grid; and   
     
     
         17 . A method as defined in  claim 15 , further comprising thinning said surrogate second substrate 
     
     
         18 . A method as defined in  claim 15 , further comprising mounting the solar cell on a support, and removing the surrogate substrate. 
     
     
         19 . A method as defined in  claim 18 , wherein the support is a rigid coverglass. 
     
     
         20 . A method of manufacturing a solar cell comprising:
 providing a first semiconductor substrate which is off-cut from a crystal plane by at least 6° towards the (111)A plane:   forming a top subcell on said substrate and lattice matched therewith having a band gap in the range of 1.8 to 2.1 eV;   forming a middle subcell over said top subcell and lattice matched therewith, having a band gap in the range of 1.2 to 1.8 eV; and   forming a bottom subcell over said middle subcell and lattice mismatched therewith, having a band gap in the range of 0.7 to 1.2 eV.   
     
     
         21 . The method as defined in  claim 20 , wherein the top subcell is composed of InGa(Al)P. 
     
     
         22 . The method as defined in  claim 20 , wherein said middle cell is composed of a GaInP, GaAs. GaInAs, GaAsSb, or GaInAsN emitter region and a GaAs, GaInAs, GaAsSb, or GaInAsN base region. 
     
     
         23 . The method as defined in  claim 22 , wherein the middle subcell is composed of an InGaP emitter layer and a GaAs or an In 0.015 GaAs base layer. 
     
     
         24 . The method as defined in  claim 20 , wherein the bottom subcell is composed of InGaAs base and emitter regions. 
     
     
         25 . A method as defined in  claim 20 , further comprising a graded interlayer disposed between said middle subcell and said bottom subcell, said interlayer being compositionally graded to lattice match the middle subcell on one side and the bottom subcell on the other side. 
     
     
         26 . The method as defined in  claim 25 , wherein said graded interlayer is composed of any of any of the As, P, N, Sb based III-V compound semiconductors subject to the constraints of having the in-plane lattice parameter greater or equal to that of the middle subcell and less than or equal to that of the bottom subcell, and having a band gap energy greater than that of the middle subcell. 
     
     
         27 . The method as defined in  claim 25 , wherein the graded interlayer is composed of (In x Ga 1-x ) y Al 1-y As, with x and y selected such that the band gap of the interlayer remains constant at approximately 1.50 eV. 
     
     
         28 . A method of forming a multijunction solar cell comprising:
 providing a first semiconductor substrate which is off-cut from the (001) crystal plane by at least 6° towards the (111)A plane; and   forming a first top subcell including base and emitter layers composed of InGaP or InGa(Al)P semiconductor material, respectively, on said first substrate.   
     
     
         29 . A method as defined in  claim 28 , further comprising;
 forming a second subcell formed of GaAs semiconductor material over said first subcell.   
     
     
         30 . A method as defined in  claim 29 , further comprising:
 forming a third bottom subcell over said second subcell and lattice mismatched therewith.   
     
     
         31 . A method as defined in  claim 30 , further comprising:
 forming a lattice constant transition material positioned between the second subcell and the third subcell, said lattice constant transition material having a lattice constant that changes gradually from the lattice constant of the second subcell to the lattice constant of the third subcell.   a grading interlayer disposed over said second solar subcells and having a third band gap greater than said second band gap; and   a third solar subcell disposed over said grading interlayer that is lattice mismatched with respect to said middle subcell and having a fourth band gap smaller than said third band gap.   
     
     
         32 . A solar cell as defined in  claim 28 , wherein said substrate is off-cut by 15° towards the (111)A plane. 
     
     
         33 . A solar cell as defined in  claim 28 , wherein said substrate is selected from the group consisting of germanium or GaAs. 
     
     
         34 . A solar cell as defined in  claim 15 , wherein said first solar subcell is composed of an InGa(Al)P emitter region and an InGa(Al)P base region. 
     
     
         35 . A solar cell as defined in  claim 15 , wherein said second solar subcell is composed of an InGaP emitter region and an In 0.015 GaAs or GaAs base region. 
     
     
         36 . A solar cell as defined in  claim 15 , wherein said third solar subcell is composed of an InGaAs emitter layer and an InGaAs base layer. 
     
     
         37 . A photovoltaic solar cell comprising:
 top subcell including base and emitter layers composed of InGaP or InGa(Al)P semiconductor material, grown on a GaAs substrate having an off-cut from the (001) plane by at least 6° in the direction of the (111)A plane.   
     
     
         38 . A solar cell as defined in  claim 21 , further comprising a bottom subcell disposed over a substrate selected from the group of GaAs, Ge, Si, or sapphire. 
     
     
         39 . A solar cell as defined in  claim 22 , wherein said bottom subcell is bonded to said substrate by an adhesive. 
     
     
         40 . A solar cell as defined in  claim 22 , wherein the bottom subcell is eutectically bonded to GaAs, Ge, or Si substrate. 
     
     
         41 . A solar cell as defined in  claim 21 , further comprising a middle subcell composed of GaAs. 
     
     
         42 . A solar cell as defined in  claim 22 , wherein a middle solar subcell disposed between said topcell and said bottom cell is composed of an InGaP emitter region and an In 0.015 GaAs or GaAs base region. 
     
     
         43 . A solar cell as defined in  claim 22 , wherein said bottom subcell is composed of an InGaAs emitter layer and an InGaAs base layer. 
     
     
         44 . A solar cell as defined in  claim 21 , wherein said top subcell has a first band gap; and further comprising a second subcell over said first solar subcell having a second band gap smaller than said first band gap; a grading interlayer over said second solar cell, said grading interlayer having a third band gap greater than said second band gap; and a third solar subcell over said grading interlayer having a fourth band gap smaller than said second band gap such that said third subcell is lattice mismatched with respect to said second subcell.